Shunt systems for directing body fluid from one region to another are known in the medical field. One application for such a fluid shunt system is in the treatment of hydrocephalus in order to direct cerebrospinal fluid away from the brain and into the venous system or to another region of the body. In this application, a shunt is implanted on the patient's skull, under the scalp, and is coupled to a brain ventricle catheter which is adapted for insertion into the brain and to a distal catheter which is adapted for insertion into the drainage region, such as the peritoneal cavity, the atrium or other drainage site.
Generally, fluid shunt systems include a valve mechanism for controlling, or regulating the fluid flow rate. Illustrative valve mechanisms operate to permit fluid flow only once the fluid pressure reaches a certain level and may permit adjustment of the pressure level at which fluid flow commences.
One such adjustable valve, described in U.S. Pat. No. 4,551,128 (Hakim et al.), includes a flexible diaphragm and plate positioned to divide a housing into inlet and outlet chambers which communicate through an aperture in the plate. A valve element is biased against the aperture to close the aperture until the fluid pressure in the inlet chamber exceeds a preselected "popping pressure." The popping pressure is adjustable by adjusting an external screw of the valve. However, due to the elastomeric properties of the diaphragm material, maintenance of the implanted valve may be required. Further, flow rate adjustment of the Hakim et al. device after implantation may require a surgical procedure.
Another adjustable valve mechanism, described in U.S. Pat. No. 4,781,673 (Watanabe), includes two parallel fluid flow passages, with each passage including a flow rate regulator and an on-off valve. Fluid flow through the passages is manually controlled by palpably actuating the on-off valves through the scalp. Although the Watanabe device permits flow rate control palpably through the scalp and thus, without surgical intervention, patient and/or physician attention to the valve settings is required.
Effective fluid flow rate control is particularly important since overdrainage of cerebrospinal fluid can result in dangerous conditions, including subdural hematoma. Overdrainage tends to occur when a patient moves from a horizontal position to a sitting or standing position, due to a siphon effect in the shunt system. In order to reduce the risk of overdrainage, some shunt systems include additional devices, sometimes referred to as anti-siphon devices, for preventing overdrainage. Some such devices use weights, which move in response to the patient changing position, to open or close the fluid flow path. One system, described in U.S. Pat. No. 5,368,556 (Lecuyer), includes spherical weights which provide additional compressive force against a valve spring to help maintain the valve in a closed position when the patient is sitting or standing. However, noise associated with the use of such weights may be objectionable.